Even though there has been considerable study of alternative electrochemical systems, the lead-acid battery is still the battery-of-choice for general purpose uses such as starting a vehicle, boat or airplane engine, emergency lighting, electric vehicle motive power, energy buffer storage for solar-electric energy, and field hardware whether industrial or military. These batteries may be periodically charged from a generator.
The conventional lead-acid battery is a multi-cell structure. Each cell contains a plurality of vertical positive and negative plates formed of lead-based alloy grids containing layers of electrochemically active pastes. The paste on the positive plate contains lead oxide which is a positive active material and the negative plates contain a negative active material such as sponge lead. This battery has been widely used in the automotive industry for many years and there is substantial experience and tooling in place for manufacturing this battery and its components and the battery is based on readily available materials, is inexpensive to manufacture, and is widely accepted by consumers.
However, the lead-acid battery has several limitations. Electrolyte stratification commonly occurs due to vertical orientation of the plates reducing battery performance. Stirring of the electrolyte by circulation or mixing is complex, unreliable and expensive. The vertical orientation and the expansion and contraction of the active materials during charging and discharging cycles leads to shedding and flaking of conductive particles of the paste which accumulate at the bottom of the cell. In fact, conventional batteries contain a sedimentation well to receive the flake particles. Eventually, enough of these particles collect to form a bridge connecting and short circuiting the electrodes and shortening useful life of the battery.
The electrochemistry of the conventional lead-acid battery results in formation of gases. The buildup of pressure requires provision of a vent cap for each cell which permits evaporation of water from the dilute sulfuric acid electrolyte. Another limitation of conventional lead-acid batteries is high internal resistance which causes decreased energy and power output and non-uniform current density in the plates which leads to shortened life of active materials.
Various improvements have been suggested to improve battery design and performance. Prince (U.S. Pat. No. 1,069,809), Wilson (U.S. Pat. No. 1,126,671), Steig (U.S. Pat. No. 4,138,533) and Deseniss (U.S. Pat. No. 3,429,747) provide multiple tabs or lugs on vertical plates to achieve more equal collection of current. Prince only utilizes two end lugs on the negative grids and one central lug on the positive grids. Wilson requires a copper insert and the electrodes in the Deseniss battery are in a rolled, spiral configuration.
Silvey (U.S. Pat. No. 540,076) discloses a battery containing a stack of horizontal plates. Each plate is separated by a porous, absorbent fabric. Glass wool separators are utilized in the vertical plate battery disclosed by Powers (U.S. Pat. No. 2,428,470). Huffman et al (U.S. Pat. No. 3,310,438) and Wheadon et al (U.S. Pat. No. 3,881,952) use expanded metal sheets as the central grid for forming plate electrodes and Smith (U.S. Pat. No. 3,821,029) provides an aperture in the cell partition for connecting conductors of adjacent cells.
Though these separate structures individually improve the performance of the diverse battery configurations, they do not provide a low cost, high performance, long-life lead-acid battery suitable for deep cycle applications.